Abstract: The effect of different homogenizing treatments on the microstructure and properties of an Al-Zn-Mg-Sc alloy was a studied by conductivity measuring, room temperature tensile property testing, scanning electron microscopy and transmission electron microscopy, et al. The results show that the as-cast Al-Zn-Mg-Sc alloy was a supersaturated solid solution, and the alloy elements segregated along grain boundaries to form the non-equilibrium eutectic T phase rich in Zn and Mg and the impurities rich in Fe, Si and Mn. When the homogenizing temperature was 350 ℃, the equilibrium phase η-MgZn2 precipitated from the supersaturated matrix. With the increase of homogenizing temperature, non-equilibrium eutectic T phase gradually dissolved into the matrix, the conductivity decreased and a lot of Al3(Sc, Zr) particles precipitated from the grains, and the thermal working property of the alloy increased. The fairly suitable homogenizing treatment precedure of the tested alloy was 470 ℃×12 h.